Looks like the best way to get the message to MTA bus drivers who text or gab on the phone behind the wheel is pretty old-fashioned — just threaten to fire them.

The number of bus drivers caught using their cellphones on the job has dropped dramatically — to just eight — since Jan. 1, when the MTA toughened penalties calling for the dismissal of some repeat offenders, a transit official said yesterday.

Before that, the MTA issued about 30 violations a month for cellphone use, an official said. In the two-year stretch from 2009 to 2010 before a first crackdown on driver cellphone use, the MTA issued a whopping 647 violations. “If we can sustain this, we’ll have a really good year,” said Stephen Vidal, bus-safety and -training chief at NYC Transit.